This invention relates to the manner of generating, controlling, and distributing electrical power from an electrical generator driven by an internal combustion engine. The generated electrical power is used to power computer-controlled electric motors used as the traction drive in multipurpose lightweight mowers, and to provide power to on-board mower attachments and external electrical equipment.
Lightweight mowers exist today in numerous configurations and are purposefully built to meet the application needs related to the industry in which they are used. Typical examples of these mowers are: Ride on Lawn Mowers; Yard and Garden Tractors; Snow Blowers; Golf Carts and Utility Carts; Traffic/Parking Police Scooters; Postal Delivery Vehicles; Airport People Movers; Airport Tarmac Shuttle Vehicles; Disabled-Person Movers; Hybrid Electric Vehicles; Go-carts; and All-Terrain Vehicles. These vehicles require a power source that is typically directly or indirectly mechanically linked to the drive wheels for traction and some vehicles are provided with a mechanical connection for powering onboard attachments and externally attached devices. Drive power trains typically have used drive axles, chain/sprocket drives, manual gear-selection transmissions, hydrostatic transmissions, differential gears, etc. in varying combinations. Steering and speed control techniques vary between the different types of vehicles. Most of the vehicles use a mechanical differential in the drive train to balance the torque applied to the driven wheels so that the wheels can rotate at different speeds when they are required to make a turn.
The power sources for the listed vehicles have been either battery-powered electric motors or internal combustion motors. Both of these sources have shortcomings when they are used separately in a drive system.
Negative features of battery-powered motor driven vehicles have been the battery charge cycle, battery life, battery weight, space required for the batteries, and replacement costs of batteries. Many tasks cannot be completed without the batteries having to be recharged due to the length of operational time required or due to the batteries not being fully recharged. The charging time required can be excessive. The weight of the batteries adds to the load on the drive and a large space is required on the vehicle for mounting the batteries.
The internal combustion engine has features that detract from its use in directly driving a transmission and differential. Low output torque at low speed and decreasing torque beyond an optimum speed somewhere below maximum speed occurs in this engine. A typical engine will have a range of speeds up to 3300 RPM but torque efficiency will be maximized between 2500 and 2800 RPM. The loss of efficiency increases the thermal dissipation in the engine which causes fatiguing and failure of engine components. At low speeds, excessive vibration of the engine is also a problem. Continual operation of the internal combustion engine at its most efficient speed is desirable, but converting the fixed input speed from the engine to a variable speed output from the transmission is not efficient.
With the advent of solid-state power-switching devices such as MOSFETs (metal oxide semiconductor field effect transistors) and IGBTs (insulated-gate bipolar transistors) and microprocessors, the electronic controls for generators and motors that were very complex and expensive in the past, have become economically practical. Today, the electric generator/motor drive provides the flexibility in control and the ruggedness in assembly needed for a small electric motor-driven vehicle. Thus, an improved innovative small vehicle drive system has been developed with an electric generator driven by an internal combustion engine and an electric motor that provides high output torque up to its base speed. The generator supplies electrical power through a power control module to the motor/gearbox on each driven wheel and may provide external power through 110/120V AC and 12V outlets.